1. Field of the Invention
The present invention relates to an air conditioning apparatus for a vehicle, which includes a heating heat exchanger and electric heating members integrated with the heating heat exchanger. More particularly, the present invention relates to a control unit for electrically controlling the electric heating members.
2. Description of Related Art
In recent years, it is desired to improve an efficiency of an engine in an engine compartment. When the efficiency of the engine is improved, a load of the engine is decreased, and cooling water for cooling the engine can not be sufficiently heated. Therefore, in a hot-water type air conditioning apparatus where air blown toward a passenger compartment is heated using the engine cooling water, there is a problem that heating capacity for the passenger compartment is insufficient.
To overcome the problem, JP-A-5-69732 proposes a hot water type heating heat exchanger integrated with an electric heating member. In the heating heat exchanger, when a temperature of hot water flowing through the heating heat exchanger is lower than a set temperature, electric power is supplied to the electric heating member to heat air using heat generated in the electric heating member. However, in the heating heat exchanger, because electric power supplied to the electric heating member is simply switched according to the temperature of water, the heating capacity for the passenger compartment cannot be controlled finely according to a driving state of a vehicle and the other conditions in the vehicle. Further, because the electric heating member is integrated with the heating heat exchanger, heat generated in the electric heating member is transmitted to the water flowing through the heating heat exchanger when the water has a low temperature; and therefore, air blown toward the passenger compartment cannot be effectively heated by heat generated in the electric heating member.